The use of antibodies in sensitive immunoassays provides a means of detecting carcinogens adducted to DNA. In population studies, monoclonal antibody technology is a useful tool in developing reagents to detect these chemical structures. Using different monoclonal antibodies that detect different epitopes of aflatoxin adducted to DNA, patterns of reactions appear to detect different metabolic products of this carcinogen. Hetero-antibodies for benzo(a)pyrene (BP)-DNA adducts have been used to identify BP-DNA in individuals who by occupations have been exposed to high levels of these compounds. Monoclonal antibodies to alter carcinogens adducted to DNA are being developed. Serum from some individuals has clearly demonstrated antibodies to BP-DNA. It is, therefore, important to develop a system of production of human monoclonal antibodies. To this end, a number of established myeloma and B-cell lines have been screened for the capability to be fused with human B cells. A model system has been established whereby chronic lymphocytic leukemia cells have been fused to a human myeloma cell line. The product of this cell line was the predominant cell surface immunoglobulin found on the chronic lymphocytic leukemia cells. This immunoglobulin was then used to produce a monoclonal antibody selected on the basis of restricted reactions to the specific immunoglobulin. Thus an anti-idiotype monoclonal antibody has been produced. The results demonstrate the capability of using human materials, B cells, and myeloma cell lines to produce monoclonal antibodies.